The coefficient of thermal expansion (CTE) of a polymer material—specifically, an epoxy resin—is about 50 to 80 ppm/° C., significantly higher several to tens of times than the CTE of a ceramic material such as inorganic particles or a metal material, (for example, the CTE of silicon is 3 to 5 ppm/° C., and the CTE of copper is 17 ppm/° C.). Thus, when a polymer material is used in conjunction with an inorganic material or a metal material in a semiconductor, a display, or the like, the properties and processability of the polymer material are significantly degraded due to the CTE-mismatch of the polymer material and the inorganic material or the metal material. In addition, during semiconductor packaging in which a silicon wafer and a polymer substrate are used in parallel, or during a coating in which a polymer film is coated with an inorganic barrier layer to impart gas barrier properties, product defects such as the generation of cracks in an inorganic layer, the warpage of a substrate, the peeling of a coating layer, the failure of a substrate, and the like, may be generated due to a high CTE-mismatch between constituent elements upon the changes in processing and/or applied temperature conditions.
Because of the high CTE of the polymer material and the resultant dimensional change of the polymer material, the development of technologies such as next generation semiconductor substrates, printed circuit boards (PCBs), packaging, organic thin film transistors (OTFTs), and flexible display substrates may be limited. Particularly, currently, in the semiconductor and PCB fields, designers are facing challenges in the design of next generation parts requiring high degrees of integration, miniaturization, flexibility, performance, and the like, in securing processability and reliability in parts due to polymer materials having significantly high CTEs as compared to metal/ceramic materials. In other words, due to the high thermal expansion properties of polymer materials at processing temperatures, defects may be generated, processability may be limited, and the design of parts and the securing of processability and reliability therein may be objects of concern. Accordingly, improved thermal expansion properties or dimensional stability of the polymer material are necessary in order to secure processability and reliability in electronic parts.
To date, in order to improve thermal expansion properties, i.e. to obtain a low CTE value in a polymer material such as an epoxy resin, (1) a method of producing a composite of an epoxy resin with inorganic particles (an inorganic filler) and/or fabrics and (2) a method of designing and synthesizing a novel epoxy resin having a decreased CTE have been used.
When the composite of the epoxy compound and the inorganic particles as the filler is formed in order to improve thermal expansion properties, a large amount of inorganic silica particles, having a diameter of about 2 to 30 μm is required in order to decrease the CTE sufficiently. However, due to the addition of the large amount of inorganic particles, the processability and performance of the parts may be deteriorated. That is, the presence of the large amount of inorganic particles may decrease fluidity, and voids may be generated during the filling of narrow spaces. In addition, the viscosity of the material may increase exponentially due to the addition of the inorganic particles. Further, the size of the inorganic particles tends to decrease due to the miniaturization of semiconductor structures. When a filler having a particle size of 1 μm or less is used, a decrease in fluidity (increase in viscosity) may be intensified. When inorganic particles having a large average particle diameter are used, the frequency of insufficient filling in the case of a composition including a resin and the inorganic particles may increase. While the CTE of the composite may be decreased significantly when a composition including an organic resin and a fiber as the filler is used, the CTE of fiber composite is still high as compared to that of a silicon chip or the like.
As described above, the manufacturing of highly integrated and high performance electronic parts for next generation semiconductor substrates, PCBs, and the like, may be restricted due to limitations in the composite technology of epoxy resins. Thus, the development of an epoxy composite having improved heat resistance properties—namely, a low CTE and a high glass transition temperature—is required to overcome a lack of heat resistance properties due to a high CTE and poor processability of a common thermosetting polymer composite.